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- Analytical approach (1)
- Axle inspection (1)
- Composite (1)
- Material characterisation (1)
- Phased Array (1)
- Purity grade (1)
- THz SAFT Optical layer reconstruction (1)
- Ultrasonic immersion tank testing (1)
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- Ultrasound (1)
For in-service inspections on wheelset axles with a hollow drilling, mechanized ultrasound inspection systems with single element probes are typically used. The ultrasonic testing in the zones close to the external surface of the railway axles can be realized from the inside of the bore hole, without demounting the wheelset and without dismantling the wheels and the brake discs. The testing system must be able to find flaws in the external surface of the hollow shafts, whose surface lies in the radial-radial plane, these are called transversal flaw. Presently testing systems are used, where scanning is realized in the circumferential direction by mechanical rotation of the probe system in the actual drilling. The phased array probe system, which is presented here, can carry out the rotation scan electronically. The scan can be carried out by simply moving the system forward and backwards through the drilling without mechanical rotation. Manipulation becomes simpler and the inspection time can be shortened considerably. The ultrasonic beam can be inclined exactly and be focused in the plane vertical to the specimen axis.
The probe is designed with help of indispensable simulations using especially designed software developed by BAM. The feasibility and the alignment between the simulated and experimental results were shown in earlier projects reported by Boehm et al. (2006) and Völz et al. (2012). The main task here is to optimize a probe for bore holes with a diameter of 65 mm with an increase in sensitivity and a high spatial resolution. This development will be carried out by use of extensive simulations and result in certain changes of the relevant probe parameters.
With increased usage of highly demanded, modern materials on safety
relevant parts (e.g. railway wheel sets, generator shafts, turbine disks, medical
implants, etc.) comprehensive analyses regarding the quality of the material are
requested. This gives a focus to non-destructive methods using ultrasound immersion
tank testing for classifying the degree of purity. Two autonomous standards,
ASTM E588 and SEP 1927, have been established for the definition, execution and
evaluation for this high resolution ultrasonic measurements on steel products.
The propagation of ultrasonic waves and the resulting sound field are strongly
dependent on the acoustical properties of the inspected material and the geometry
of probes and specimen. The definition of the measurement setup and the evaluation
methods appear to differ significantly in the given standards. ASTM E588 and
SEP 1927 prescribe the requirement for surface roughness and probe selection, are
using threshold based methods for cleanliness detection, but differ in computation
for the degree of purity. This has been the motivation for a comparison between
both standards with the main focus on amplitude depth dependency and overall spatial
resolution taking the influence of different material characteristics, geometry of
the specimen and sound fields into account.
A performance comparison between the use of non-focusing and focusing probes
respective to the threshold based detection will be presented in this contribution. In
addition, the usage of complex reconstruction algorithms (e.g. SAFT, echo tomography)
is compared with the traditional approaches of inclusion detection and
estimation of the degree of purity
Electromagnetic waves with frequencies between 0.1 and 10 THz are described as THz-radiation (T-ray). The ability to penetrate dielectric materials makes T-rays attractive to reveal discontinuities in polymer and ceramic materials. THz-Time Domain Spectroscopy Systems (THz-TDS) are available on the market today which operates with THz-pulses transmitted and received by optically pumped semiconductor antennas. In THz-TDS the travelling time (ToF) and shape of the pulse is changed if it interacts with the dielectric material and its inherent discontinuities.
A tomogram of the object under the test can be reconstructed from time of flight diffraction (ToFD) scans if a synthetic focusing aperture (SAFT) algorithm is applied. Otherwise, planar discontinuities like cracks in plastics or delaminated layers in composites can be abstracted as layers located at any angle in relation to the outer sample surface direction. A tomogram from the scanned sample can then be reconstructed in case the interactions of electromagnetic pulses with the existing inherent interfaces are detectable and a model is assumed which describes the device under the test as multilayer structure composed of thin layers with different dielectric properties.
A short description of both the SAFT – and Optical Layer algorithm for the reconstruction of the inherent structure is initially given. Measurements on representative samples with a variety of artificially produced small and large scale. Reconstructed tomograms are presented to discuss and evaluate the benefits and limits of the two different reconstruction approaches.
Applications of fibre reinforced plastic (FRP) composites in modern industries are increasing due to their considerable advantages such as light weight and excellent mechanical properties. Accordingly, importance of operational safety of modern structures made of advanced composites by ensuring the material quality has led to increasing demands for development of non-destructive evaluation (NDE) systems. In the context of a European project entitled “Validated Inspection Techniques for Composites in Energy Applications” (VITCEA), the aim is to develop and validate traceable procedures for novel NDE techniques with contrasting damage detection capabilities in energy related applications such as wind and marine turbine blades, nacelles, oil and gas flexible risers. Accordingly, VITCEA focuses on optimization of ultrasonic tests (UTs) for quantitative defect detection and quality characterization of FRP structures. In this context, the present study describes the ultrasound field in heterogeneous composite materials. The theoretical predictions are compared with simulation results obtained from CIVA a software package dedicated to NDT simulations based on the asymptotic ray theory.